Classifications

• • C—CHEMISTRY; METALLURGY
  • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
  • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
  • C23C18/00—Chemical coating by decomposition of either liquid compounds or solutions of the coating forming compounds, without leaving reaction products of surface material in the coating; Contact plating
  • C23C18/16—Chemical coating by decomposition of either liquid compounds or solutions of the coating forming compounds, without leaving reaction products of surface material in the coating; Contact plating by reduction or substitution, e.g. electroless plating
  • C23C18/31—Coating with metals
  • C23C18/38—Coating with copper
  • C23C18/40—Coating with copper using reducing agents
  • C23C18/405—Formaldehyde
• • C—CHEMISTRY; METALLURGY
  • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
  • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
  • C23C18/00—Chemical coating by decomposition of either liquid compounds or solutions of the coating forming compounds, without leaving reaction products of surface material in the coating; Contact plating
  • C23C18/16—Chemical coating by decomposition of either liquid compounds or solutions of the coating forming compounds, without leaving reaction products of surface material in the coating; Contact plating by reduction or substitution, e.g. electroless plating
  • C23C18/1601—Process or apparatus
  • C23C18/1633—Process of electroless plating
  • C23C18/1675—Process conditions
• • C—CHEMISTRY; METALLURGY
  • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
  • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
  • C23C18/00—Chemical coating by decomposition of either liquid compounds or solutions of the coating forming compounds, without leaving reaction products of surface material in the coating; Contact plating
  • C23C18/16—Chemical coating by decomposition of either liquid compounds or solutions of the coating forming compounds, without leaving reaction products of surface material in the coating; Contact plating by reduction or substitution, e.g. electroless plating
  • C23C18/18—Pretreatment of the material to be coated
  • C23C18/20—Pretreatment of the material to be coated of organic surfaces, e.g. resins
  • C23C18/28—Sensitising or activating
  • C23C18/30—Activating or accelerating or sensitising with palladium or other noble metal
• • C—CHEMISTRY; METALLURGY
  • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
  • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
  • C23C18/00—Chemical coating by decomposition of either liquid compounds or solutions of the coating forming compounds, without leaving reaction products of surface material in the coating; Contact plating
  • C23C18/16—Chemical coating by decomposition of either liquid compounds or solutions of the coating forming compounds, without leaving reaction products of surface material in the coating; Contact plating by reduction or substitution, e.g. electroless plating
  • C23C18/31—Coating with metals
  • C23C18/38—Coating with copper
  • C23C18/40—Coating with copper using reducing agents

Definitions

• the present invention is directed to electroless copper plating compositions and methods for electroless plating copper on substrates, wherein electroless copper plating has a high electroless copper plating rate at low temperatures and the electroless copper plating compositions are stable. More specifically, the present invention is directed to electroless copper plating compositions and methods for electroless plating copper on substrates, wherein electroless copper plating has a high electroless copper plating rate at low temperatures and the electroless copper plating compositions are stable, wherein the electroless copper plating compositions include pyridinium compounds or salts thereof.
• Electroless copper plating baths are in widespread use in metallization industries for depositing copper on various types of substrates.
• the electroless copper baths are used to deposit copper on walls of through-holes and circuit paths as a base for subsequent electrolytic copper plating.
• Electroless copper plating also is used in the decorative plastics industry for deposition of copper on nonconductive surfaces as a base for further plating of copper, nickel, gold, silver and other metals, as required.
• Electroless copper baths which are in commercial use today contain water soluble divalent copper compounds, chelating agents or complexing agents, for example, Rochelle salts and sodium salts of ethylenediamine tetraacetic acid, for chelating the divalent copper ions, reducing agents, for example, formaldehyde, and formaldehyde precursors or derivatives, and various addition agents to make the bath more stable, adjust the plating rate and brighten the copper deposit.
• chelating agents or complexing agents for example, Rochelle salts and sodium salts of ethylenediamine tetraacetic acid
• reducing agents for example, formaldehyde, and formaldehyde precursors or derivatives
• electroless copper plating baths the components are continuously consumed such that the baths are in a constant state of change, thus consumed components must be periodically replenished. Control of the baths to maintain high plating rates with substantially uniform copper deposits over long periods of time is exceedingly difficult.
• electroless copper plating rates of equal to or greater than 0.6 ⁇ m/5 min. are highly desirable (preferably desired for current horizontal plating applications) but rarely achieved, especially at low electroless plating temperatures, such as below 40 °C.
• Consumption and replenishment of bath components over several metal turnovers (MTO) can also contribute to bath instability, for example, through the buildup of side products. Therefore, such baths, and particularly those having a high plating potential, i.e.
• electroless copper bath instability can result in nonuniform or discontinuous copper plating along a surface.
• Such discontinuity of the copper deposit can ultimately lead to mal-functioning of any electrical device in which the defective printed circuit board is included.
• stabilizers which have been used in electroless copper plating baths are sulfur containing compounds, such as disulfides and thiols.
• sulfur containing compounds such as disulfides and thiols.
• many stabilizers lower electroless copper plating rates, and, also, at high concentrations can be catalyst poisons, thus reducing plating rates or inhibiting plating and compromising the performance of the plating bath.
• Low plating rates are detrimental to electroless copper plating performance.
• Electroless copper plating rate is also temperature dependent, thus when high stabilizer concentrations lower the rate, increasing the plating temperature can increase the rate.
• an "accelerator" additive can be incorporated into the electroless bath formulation.
• the accelerator additive does not impact the stability of the electroless bath, such that higher plating rates can be achieved while keeping bath stability in check; or such that the same plating rate is now achieved at lower temperatures which typically also results in a more stable bath.
• the lower electroless bath temperatures reduce cost of the electroless bath, for example, by decreasing the rate of passive consumption of plating chemicals.
• a more stable formulation which is afforded by lowering the working temperature, results in lower maintenance requirements.
• lower plating temperatures can lower the build-up of internal stress in the electroless deposit, making the metallization process better suited for high-adhesion applications.
• rate acceleration in electroless copper plating is a key strategy for lowering working temperatures, lowering internal stress of copper deposits such as on flexible substrates and decreasing overall running costs of metallization.
• the present invention is directed to an electroless copper plating composition including one or more sources of copper ions, one or more pyridinium compounds, one or more complexing agents, one or more reducing agents, and, optionally, one or more pH adjusting agents, wherein a pH of the electroless copper plating composition is greater than 7.
• the present invention is also directed to a method of electroless copper plating including:
• the pyridinium compounds enable increased electroless copper plating rates at low plating temperatures of less than or equal to 40 °C.
• the electroless copper plating compositions and methods of the present invention further enable good through-hole wall coverage, even at low plating temperatures. Low plating temperatures reduce consumption of electroless copper plating composition additives which occur by undesired side reactions or by decomposition, thus providing a more stable electroless copper plating composition, and lower the cost of operating the electroless copper plating process.
• the electroless copper plating compositions of the present invention are stable over wide concentration ranges of the pyridinium compounds.
• a broad operating window for the pyridinium compounds concentration means that the pyridinium compounds concentrations do not need to be carefully monitored such that the performance of the electroless copper plating compositions do not substantially change regardless of how the composition components are being replenished and consumed.
• composition and “bath” are used interchangeably throughout this specification.
• alkyl unless otherwise described in the specification as having substituent groups, means an organic chemical group composed of only carbon and hydrogen and having a general formula: C n H 2n+1 .
• average is equivalent to the mean value of a sample. All amounts are percent by weight, unless otherwise noted. All numerical ranges are inclusive and combinable in any order except where it is logical that such numerical ranges are constrained to add up to 100%.
• the electroless copper plating compositions of the present invention include one or more sources of copper ions, one or more pyridinium compounds, one or more complexing agents; one or more reducing agents; water; and, optionally, one or more pH adjusting agents, wherein a pH of the electroless copper plating composition is greater than 7.
• the one or more pyridinium compounds have a formula: wherein R 1 is selected from the group consisting of linear or branched, substituted or unsubstituted (C 1 -C 10 )alkyl, substituted or unsubstituted (C 6 -C 10 )aryl, substituted or unsubstituted (C 6 -C 10 ) heterocyclic aromatic groups and substituted or unsubstituted benzyl, wherein substituent groups are selected from the group consisting of hydroxyl, sulfate, amino, amide, carbonyl and carboxyl; and R 2 is selected from the group consisting of hydrogen, hydroxyl, sulfate, carbonyl, carboxyl, vinyl, amino and amide.
• R 1 is selected from the group consisting of linear or branched, substituted and unsubstituted (C 2 -C 4 )alkyl and substituted or unsubstituted C 6 -heterocyclic aromatic group, wherein the substituent groups are selected from the group consisting of hydroxyl and sulfate; and, more preferably, R 2 is selected from the group consisting of hydrogen, hydroxyl and sulfate; and, most preferably, R 1 is selected from the groups consisting of linear, substituted or unsubstituted (C 2 -C 4 )alkyl, wherein a preferred substituent is sulfate; and, most preferably, R 2 is hydrogen.
• the pyridinium compound of formula (I) includes a counter anion to neutralize the positive charge of the pyridinium compound.
• the foregoing pyridinium compounds are hydroxide salts, sulfate, tetrafluoroborate, hexafluorophosphate, nitrate, formate, acetate, tartrate or halogen salts, wherein the halogen is selected from the group consisting of chloride, bromide, fluoride and iodide. More preferably, the salts are halogens selected from the group consisting of chloride and bromide, most preferably, the halogen is chloride.
• Examples of three preferred pyridinium compounds of the present invention are the salts 1-butylpyridinium chloride, and 1-(3-sulfopropyl) pyridinium hydroxide inner salt (also known as 1-(3-sulfopropyl) pyridinium) and 1-(4-pyridyl) pyridinium chloride.
• the pyridinium compounds of the present invention are included in amounts of 0.5 ppm or greater, preferably, from 1 ppm to 50 ppm, more preferably, from 2 ppm to 30 ppm, even more preferably, from 2.5 ppm to 20 ppm, most preferably, from 5 ppm to 20 ppm.
• Sources of copper ions and counter anions include, but are not limited to, water soluble halides, nitrates, acetates, sulfates and other organic and inorganic salts of copper. Mixtures of one or more of such copper salts can be used to provide copper ions. Examples are copper sulfate, such as copper sulfate pentahydrate, copper chloride, copper nitrate, copper hydroxide and copper sulfamate.
• the one or more sources of copper ions in the electroless copper plating composition of the present invention range from 0.5 g/L to 30 g/L, more preferably, from 1 g/L to 25 g/L, even more preferably, from 5 g/L to 20 g/L, further preferably, from 5 g/L to 15 g/L, and most preferably, from 10 g/L to 15 g/L.
• Complexing agents include, but are not limited to, sodium potassium tartrate, sodium tartrate, sodium salicylate, sodium salts of ethylenediamine tetraacetic acid (EDTA), nitriloacetic acid and its alkali metal salts, gluconic acid, gluconates, triethanolamine, modified ethylene diamine tetraacetic acids, S,S-ethylene diamine disuccinic acid, hydantoin and hydantoin derivatives.
• Hydantoin derivatives include, but are not limited to, 1-methylhydantoin, 1,3-dimethylhydantoin and 5,5-dimethylhydantoin.
• the complexing agents are chosen from one or more of sodium potassium tartrate, sodium tartrate, nitriloacetic acid and its alkali metal salts, such as sodium and potassium salts of nitirloacetic acid, hydantoin and hydantoin derivatives.
• EDTA and its salts are excluded from the electroless copper plating compositions of the present invention.
• the complexing agents are chosen from sodium potassium tartrate, sodium tartrate, nitriloacetic acid, nitriloacetic acid sodium salt, and hydantoin derivates.
• the complexing agents are chosen from sodium potassium tartrate, sodium tartrate, 1-methylhydantoin, 1,3-dimethylhydantoin and 5,5-dimethylhydantoin. Further preferably, the complexing agents are chosen from sodium potassium tartrate and sodium tartrate. Most preferably, the complexing agent is sodium potassium tartrate (Rochelle salts).
• Complexing agents are included in the electroless copper plating compositions of the present invention in amounts of 10 g/l to 150 g/L, preferably, from 20 g/L to 150 g/L, more preferably, from 30 g/L to 100 g/L, even more preferably, from 35 g/L to 80 g/L, and, most preferably, from 35 g/l to 55 g/L.
• Reducing agents include, but are not limited to, aldehydes, such as, formaldehyde, formaldehyde precursors, formaldehyde derivatives, such as paraformaldehyde, borohydrides, such sodium borohydride, substituted borohydrides, boranes, such as dimethylamine borane (DMAB), saccharides, such as grape sugar (glucose), glucose, sorbitol, cellulose, cane sugar, mannitol and gluconolactone, hypophosphite and salts thereof, such as sodium hypophosphite, hydroquinone, catechol, resorcinol, quinol, pyrogallol, hydroxyquinol, phloroglucinol, guaiacol, gallic acid, glyoxylic acid, 3,4-dihydroxybenzoic acid, phenolsulfonic acid, cresolsulfonic acid, hydroquinonsulfonic acid, catecholsulfonic acid,
• the reducing agents are chosen from formaldehyde, formaldehyde derivatives, formaldehyde precursors, borohydrides and hypophosphite and salts thereof, hydroquinone, catechol, resorcinol, and gallic acid. More preferably, the reducing agents are chosen from formaldehyde, formaldehyde derivatives, formaldehyde precursors, and sodium hypophosphite. Most preferably, the reducing agent is formaldehyde.
• Reducing agents are included in the electroless copper plating compositions of the present invention in amounts of 0.5 g/L to 100 g/L, preferably, from 0.5 g/L to 60 g/L, more preferably, from 1 g/L to 50 g/L, even more preferably, from 1 g/L to 20 g/L, further preferably, from 1 g/L to 10 g/L, most preferably, from 1 g/L to 5 g/L.
• a pH of the electroless copper plating composition of the present invention is greater than 7.
• the pH of the electroless copper plating compositions of the present invention is greater than 7.5. More preferably, the pH of the electroless copper plating compositions range from 8 to 14, even more preferably, from 10 to 14, further preferably, from 11 to 13, and most preferably, from 12 to 13.
• one or more pH adjusting agents can be included in the electroless copper plating compositions of the present invention to adjust the pH of the electroless copper plating compositions to an alkaline pH.
• Acids and bases can be used to adjust the pH, including organic and inorganic acids and bases.
• inorganic acids or inorganic bases, or mixtures thereof are used to adjust the pH of the electroless copper plating compositions of the present invention.
• Inorganic acids suitable for use of adjusting the pH of the electroless copper plating compositions include, for example, phosphoric acid, nitric acid, sulfuric acid and hydrochloric acid.
• Inorganic bases suitable for use of adjusting the pH of the electroless copper plating compositions include, for example, ammonium hydroxide, sodium hydroxide, potassium hydroxide and lithium hyddroxide.
• sodium hydroxide, potassium hydroxide or mixtures thereof are used to adjust the pH of the electroless copper plating compositions, most preferably, sodium hydroxide is used to adjust the pH of the electroless copper plating compositions of the present invention.
• one or more stabilizers can be included in the electroless copper plating compositions of the present invention.
• Stabilizers include, but are not limited to 2,2'-dipyridyl and derivatives, 4,4'-dipyridyl, phenanthroline and phenanthroline derivatives, thiomalic acid, 2,2'dithiodisuccinic acid, mercaptosuccinic acid, cysteine, methionine, thionine, thiourea, benzothiazole, mercaptobenzothiazole, 2,2'-thiodiacetic acid, 3,3'-thiodipropionic acid, 3,3'-dithiodipropionic acid, thiosulfate, and glycols such as polypropylene glycol and polyethylene glycol.
• Such optional stabilizers are included in the electroless copper plating compositions of the present invention in amounts of 0.1 ppm to 20 ppm, preferably, from 0.5 ppm to 10 ppm, more preferably, from 0.5 ppm to 5 ppm, most preferably from 0.5 ppm to 2 ppm.
• one or more secondary accelerators can be included in the electroless copper plating compositions of the present invention.
• Such accelerators include, but are not limited to, several free nitrogen bases such as guanidine, guanidine derivatives, such as guanidine hydrochloride, pyridine and pyridine derivatives such as aminopyridine, di- and trialkylamines, such as trimethylamine and triethylamine, N,N,N',N'-Tetrakis(2-Hydroxypropyl)ethylenediamine, and ethylenediaminetetraacetic acid, and nickel(II) salts such as Nickel(II) sulfate.
• An example of a preferred secondary accelerator is guanidine hydrochloride.
• Such accelerators can be included in amounts of 0.1 ppm to 500 ppm, preferably, from 0.2 to 15 ppm, more preferably from, 0.3 ppm to 10 ppm, most preferably from 0.3 ppm to 5 ppm.
• one or more surfactants can be included in the electroless copper plating compositions of the present invention.
• Such surfactants include ionic, such as cationic and anionic surfactants, non-ionic and amphoteric surfactants. Mixtures of the surfactants can be used.
• Surfactants can be included in the compositions in amounts of 0.001 g/L to 50 g/L, preferably in amounts of 0.01 g/L to 50 g/L.
• Cationic surfactants include, but are not limited to, tetra-alkylammonium halides, alkyltrimethylammonium halides, hydroxyethyl alkyl imidazoline, alkyl imidazolium, alkylbenzalkonium halides, alkylamine acetates, alkylamine oleates and alkylaminoethyl glycine.
• Anionic surfactants include, but are not limited to, alkylbenzenesulfonates, alkyl or alkoxy naphthalene sulfonates, alkyldiphenyl ether sulfonates, alkyl ether sulfonates, alkylsulfuric esters, polyoxyethylene alkyl ether sulfuric esters, polyoxyethylene alkyl phenol ether sulfuric esters, higher alcohol phosphoric monoesters, polyoxyalkylene alkyl ether phosphoric acids (phosphates) and alkyl sulfosuccinates.
• Amphoteric surfactants include, but are not limited to, 2-alkyl-N-carboxymethyl or ethyl-N-hydroxyethyl or methyl imidazolium betaines, 2-alkyl-N-carboxymethyl or ethyl-N-carboxymethyloxyethyl imidazolium betaines, dimethylalkyl betains, N-alkyl- ⁇ -aminopropionic acids or salts thereof and fatty acid amidopropyl dimethylaminoacetic acid betaines.
• the surfactants are non-ionic.
• Non-ionic surfactants include, but are not limited to, alkyl phenoxy polyethoxyethanols, polyoxyethylene polymers having from 20 to 150 repeating units and random and block copolymers of polyoxyethylene and polyoxypropylene, and polyamines, such as polyallylamine.
• one or more grain refiner can be included in the electroless copper plating compositions of the present invention.
• Grain refiners include, but are not limited to, cyanide and cyanide containing inorganic salts such as potassium hexacyanoferrate, 2-mercaptobenthiazole, 2,2'-bipyridine and 2,2'-bipyridine derivatives, 1,10-phenanthroline and 1,10-phenanthroline derivatives, vanadium oxides such as sodium Metavanadate, and nickel salts such as nickel(II) sulfate.
• Grain refiners are included in amounts well known to those of ordinary skill in the art.
• the electroless copper plating composition of the present invention consists of one or more sources of copper ions, including corresponding anions, one or more pyridinium compounds or salts thereof having formula (I), one or more complexing agents, one or more reducing agents, water, optionally, one or more pH adjusting agents, optionally, one or more stabilizers, optionally, one or more secondary accelerators, optionally, one or more surfactants, and optionally, one or more grain refiners, wherein a pH of the electroless copper plating composition is 10-14.
• the electroless copper plating composition of the present invention consists of one or more sources of copper ions, including corresponding anions, one or more pyridinium compounds or salts thereof having formula (I), wherein the salts are selected from the group consisting of hydroxide, chloride and bromide salts, one or more complexing agents, one or more reducing agents, water, one or more pH adjusting agents, one or more stabilizers, optionally, one or more secondary accelerators, optionally, one or more surfactants, and, optionally, one or more grain refiners, wherein a pH of the electroless copper plating composition is 11-13.
• the electroless copper plating compositions of the present invention consist of one or more sources of copper ions, including corresponding anions, one or more pyridinium compounds selected from the group consisting of 1-butyl pyridinium chloride, 1-(3-sulfopropyl) pyridinium hydroxide and 1-(4-pyridyl) pyridinium chloride, one or more complexing agents, one or more reducing agents, water, one or more pH adjusting agents, one or more stabilizers, optionally, one or more secondary accelerators, optionally, one or more surfactants, and, optionally, one or more grain refiners, wherein a pH of the electroless copper plating composition is 12-13.
• the electroless copper compositions and methods of the present invention can be used to electroless plate copper on various substrates such as dielectrics, semiconductors, metal-clad and unclad substrates such as printed circuit boards.
• substrates such as dielectrics, semiconductors, metal-clad and unclad substrates such as printed circuit boards.
• metal-clad and unclad printed circuit boards can include thermosetting resins, thermoplastic resins and combinations thereof, including fibers, such as fiberglass, impregnated embodiments of the foregoing.
• the substrate is a metal-clad printed circuit or wiring board with a plurality of through-holes, vias, or combinations thereof.
• the electroless copper plating compositions and methods of the present invention can be used in both horizontal and vertical processes of manufacturing printed circuit boards, preferably, the electroless copper plating compositions methods of the present invention are used in horizontal processes.
• Thermoplastic resins include, but are not limited to, acetal resins, acrylics, such as methyl acrylate, cellulosic resins, such as ethyl acetate, cellulose propionate, cellulose acetate butyrate and cellulose nitrate, polyethers, nylon, polyethylene, polystyrene, styrene blends, such as acrylonitrile styrene and copolymers and acrylonitrile-butadiene styrene copolymers, polycarbonates, polychlorotrifluoroethylene, and vinylpolymers and copolymers, such as vinyl acetate, vinyl alcohol, vinyl butyral, vinyl chloride, vinyl chloride-acetate copolymer, vinylidene chloride and vinyl formal.
• acetal resins acrylics, such as methyl acrylate
• cellulosic resins such as ethyl acetate, cellulose propionate, cellulose acetate butyrate
• Thermosetting resins include, but are not limited to allyl phthalate, furane, melamine-formaldehyde, phenol-formaldehyde and phenol-furfural copolymers, alone or compounded with butadiene acrylonitrile copolymers or acrylonitrile-butadiene-styrene copolymers, polyacrylic esters, silicones, urea formaldehydes, epoxy resins, allyl resins, glyceryl phthalates, and polyesters.
• the electroless copper plating compositions and methods of the present invention can be used to electroless copper plate substrates with both low and high T g resins.
• Low T g resins have a T g below 160° C and high T g resins have a T g of 160° C and above.
• high T g resins have a T g of 160° C to 280° C or such as from 170° C to 240° C.
• High T g polymer resins include, but are not limited to, polytetrafluoroethylene (PTFE) and polytetrafluoroethylene blends. Such blends include, for example, PTFE with polyphenylene oxides and cyanate esters.
• epoxy resins such as difunctional and multifunctional epoxy resins, bimaleimide/triazine and epoxy resins (BT epoxy), epoxy/polyphenylene oxide resins, acrylonitrile butadienesty
• the substrates are cleaned or degreased, optionally, roughened or micro-roughened, optionally, the substrates are etched or micro-etched, optionally, a solvent swell is applied to the substrates, through-holes are desmeared, and various rinse and anti-tarnish treatments can, optionally, be used.
• the substrates to be electroless copper plated with the electroless copper plating compositions and methods of the present invention are metal-clad substrates with dielectric material and a plurality of through-holes such as printed circuit boards.
• the boards are rinsed with water and cleaned and degreased followed by desmearing the through-hole walls. Prepping or softening the dielectric or desmearing of the through-holes can begin with application of a solvent swell.
• the method of electroless copper plating is for plating through-hole walls, it is envisioned that the method of electroless copper plating can also be used to electroless copper plate walls of vias.
• solvent swells can be used. The specific type can vary depending on the type of dielectric material. Minor experimentation can be done to determine which solvent swell is suitable for a particular dielectric material. The T g of the dielectric often determines the type of solvent swell to be used.
• Solvent swells include, but are not limited to, glycol ethers and their associated ether acetates. Conventional amounts of glycol ethers and their associated ether acetates well known to those of skill in the art can be used. Examples of commercially available solvent swells are CIRCUPOSITTM Conditioner 3302A, CIRCUPOSITTM Hole Prep 3303 and CIRCUPOSITTM Hole Prep 4120 solutions (available from Dow Electronic Materials).
• a promoter can be applied.
• Conventional promoters can be used.
• Such promoters include sulfuric acid, chromic acid, alkaline permanganate or plasma etching.
• alkaline permanganate is used as the promoter.
• Examples of commercially available promoters are CIRCUPOSITTM Promoter 4130 and CIRCUPOSITTM MLB Promoter 3308 solutions (available from Dow Electronic Materials).
• the substrate and through-holes are rinsed with water.
• a neutralizer is then applied to neutralize any residues left by the promoter.
• Conventional neutralizers can be used.
• the neutralizer is an aqueous acidic solution containing one or more amines or a solution of 3wt% hydrogen peroxide and 3wt% sulfuric acid.
• An example of a commercially available neutralizer is CIRCUPOSITTM MLB Neutralizer 216-5.
• the substrate and through-holes are rinsed with water and then dried.
• conditioners can be used. Such conditioners can include one or more cationic surfactants, non-ionic surfactants, complexing agents and pH adjusters or buffers. Examples of commercially available acid conditioners are CIRCUPOSITTM Conditioners 3320A and 3327 solutions (available from Dow Advanced Materials). Suitable alkaline conditioners include, but are not limited to, aqueous alkaline surfactant solutions containing one or more quaternary amines and polyamines. Examples of commercially available alkaline surfactants are CIRCUPOSITTM Conditioner 231, 3325, 813 and 860 formulations (available from Dow Electronic Materials). Optionally, the substrate and through-holes are rinsed with water.
• conditioning can be followed by micro-etching.
• Conventional micro-etching compositions can be used.
• Micro-etching is designed to clean and provide a micro-roughened metal surface on exposed metal (e.g. innerlayers and surface etch) to enhance subsequent adhesion of plated electroless copper and later electroplate.
• Micro-etches include, but are not limited to, 60 g/L to 120 g/L sodium persulfate or sodium or potassium oxymonopersulfate and sulfuric acid (2%) mixture, or generic sulfuric acid/hydrogen peroxide.
• Examples of commercially available micro-etching compositions are CIRCUPOSITTM Microetch 3330 Etch solution and PREPOSITTM 748 Etch solution (both available from Dow Electronic Materials).
• the substrate is rinsed with water.
• a pre-dip can then be applied to the micro-etched substrate and through-holes.
• pre-dips include, but are not limited to, organic salts such as sodium potassium tartrate or sodium citrate, 0.5% to 3% sulfuric acid, nitric acid, or an acidic solution of 25 g/L to 75 g/L sodium chloride.
• organic salts such as sodium potassium tartrate or sodium citrate, 0.5% to 3% sulfuric acid, nitric acid, or an acidic solution of 25 g/L to 75 g/L sodium chloride.
• An example of a commercially available pre-dip is acidic Pre-Dip CIRCUPOSITTM 6520 solution.
• a catalyst is then applied to the substrate. While it is envisioned that any conventional catalyst suitable for electroless metal plating which includes a catalytic metal can be used, preferably, a palladium catalyst is used in the methods of the present invention.
• the catalyst can be a non-ionic palladium catalyst, such as a colloidal palladium-tin catalyst, or the catalyst can be an ionic palladium. If the catalyst is a colloidal palladium-tin catalyst, an acceleration step is done to strip tin from the catalyst and to expose the palladium metal for electroless copper plating.
• an acceleration step is applied after catalyst adsorption, for example, by using hydrochloric acid, sulfuric acid or tetrafluoroboric acid as the accelerator at 0.5-10% in water to strip tin from the catalyst and to expose the palladium metal for electroless copper plating.
• the acceleration step is excluded from the method and, instead, a reducing agent is applied to the substrate subsequent to application of the ionic catalyst to reduce the metal ions of the ionic catalyst to their metallic state, such as Pd (II) ions to Pd° metal.
• CIRCUPOSITTM 3340 catalyst and CATAPOSITTM 44 catalyst available from Dow Electronic Materials
• An example of a commercially available palladium ionic catalyst is CIRCUPOSITTM 6530 Catalyst.
• the catalyst can be applied by immersing the substrate in a solution of the catalyst, or by spraying the catalyst solution on the substrate, or by atomization of the catalyst solution on the substrate using conventional apparatus.
• the catalysts can be applied at temperatures from room temperature to 80° C, preferably, from 30° C to 60° C.
• the substrate and through-holes are optionally rinsed with water after application of the catalyst.
• reducing agents known to reduce metal ions to metal can be used to reduce the metal ions of the catalysts to their metallic state.
• reducing agents include, but are not limited to, dimethylamine borane (DMAB), sodium borohydride, ascorbic acid, iso-ascorbic acid, sodium hypophosphite, hydrazine hydrate, formic acid and formaldehyde.
• Reducing agents are included in amounts to reduce substantially all of the metal ions to metal. Such amounts are well known by those of skill in the art. If the catalyst is an ionic catalyst, the reducing agents are applied subsequent to the catalyst being applied to the substrate and prior to metallization.
• the substrate and walls of the through-holes are then plated with copper using an electroless copper plating composition of the present invention.
• Methods of electroless copper plating of the present invention can be done at temperatures of 40 °C or less.
• methods of electroless copper plating of the present invention are done at temperatures from room temperature to 40 °C, more preferably, electroless copper plating is done from room temperature to 35 °C, even more preferably, from 30 °C to 35 °C, most preferably, from 30 °C to 34 °C.
• the substrate can be immersed in the electroless copper plating composition of the present invention or the electroless copper plating composition can be sprayed on the substrate.
• Methods of electroless copper plating of the present invention using electroless copper plating compositions of the present invention are done in an alkaline environment of pH greater than 7.
• methods of electroless copper plating of the present invention are done at a pH of greater than 7.5, more preferably, electroless copper plating is done at a pH of 8 to 14, even more preferably, from 10 to 14, further preferably, from 11 to 13, and most preferably, from 12 to 13.
• the electroless copper plating rates of the present invention are equal to or greater than 0.6 ⁇ m/5 min. at temperatures of less than or equal to 40 °C, more preferably, the electroless copper plating rates of the present invention are equal to or greater than 0.65 ⁇ m/5 min., such as from 0.65 ⁇ m/5 min. to 1 ⁇ m/5 min., even more preferably, equal to or greater than 0.7 ⁇ m/5 min., such as from 0.75 ⁇ m/5 min. to 1 ⁇ m/5 min., or such as from 0.75 ⁇ m/5 min. to 0.8 ⁇ m/5 min., at temperatures of less than or equal to 35 °C, most preferably, electroless plating is done at temperatures from 30 °C to 34 °C.
• the methods of electroless copper plating using the electroless copper plating compositions of the present invention enable good average backlight values for electroless copper plating of through-holes of printed circuit boards.
• Such average backlight values are preferably greater than or equal to 4.5, more preferably from 4.6 to 5, even more preferably from 4.7 to 5, most preferably from 4.8 to 5.
• Such high average backlight values enable the methods of electroless copper plating of the present invention using the electroless copper plating compositions of the present invention to be used for commercial electroless copper plating, wherein the printed circuit board industry substantially requires backlight values of 4.5 and greater.
• the electroless copper metal plating compositions and methods of the present invention enable uniform, bright copper deposits over broad concentration ranges of pyridinium compounds or salts thereof, even at high plating rates.
• All three baths include the following components:
• Each bath is used to plate copper on epoxy substrates.
• the epoxy substrates are treated as described in Example 1 in preparation for electroless copper plating. Electroless copper plating is done at 34 °C for 5 minutes. The plating rate is then determined as described in Example 1.
• the plating rate for each bath is shown in Table 3.
• the plating rate of pyridine at 2.5 ppm is higher than in the Control in Example 1, at higher concentrations of 10 ppm and 20 ppm the plating rates decline to below the plating rate of the control.
• the plating rate of pyridine is less than the Control electroless copper bath in Example 1.
• the copper deposits have a mixture of bright and uniform areas and rough and dull areas.
• All fourteen baths include the following components:
• Each bath is used to plate copper on epoxy substrates.
• the epoxy substrates are treated as described in Example 1 prior to electroless copper plating.
• Electroless copper plating is done at 34 °C for 5 minutes.
• the plating rate is determined as described above in Example 1.
• the plating rate for each bath is shown in Table 6.
• Table 6 Comparative Bath Plating Rate 4 0.61 ⁇ m/5 min. 5 0.62 ⁇ m/5 min. 6 0.57 ⁇ m/5 min. 7 0.52 ⁇ m/5 min. 8 0.48 ⁇ m/5 min.
• Even in combination with the accelerator guanidine hydrochloride the highest plating rates for the electroless copper baths containing the base pyridine are just above 0.60 ⁇ m/5 min.
• increasing the concentration of pyridine in the electroless bath shows a tendency toward a decrease in electroless copper plating rate.
• the copper deposits have bright and uniform areas intermixed with rough and dull areas.
• aqueous alkaline electroless copper compositions of the invention are prepared having the components and amounts disclosed in Table 7 below.
• TUC-662 Six (6) different FR/4 glass epoxy panels with a plurality of through-holes are provided: TUC-662, SY-1141, IT-180, 370HR, EM825 and NPGN.
• the panels are eight-layer copper-clad panels.
• TUC-662 is obtained from Taiwan Union Technology
• SY-1141 is obtained from Shengyi.
• IT-180 is obtained from ITEQ Corp.
• NPGN is obtained from NanYa and 370HR from Isola
• EM825 are obtained from Elite Materials Corporation.
• the T g values of the panels range from 140° C to 180° C. Each panel is 5cm x 10cm.
• the through-holes of each panel are treated as follows:
• Each panel is cross-sectioned nearest to the centers of the through-holes as possible to expose the copper plated walls.
• the cross-sections no more than 3 mm thick from the center of the through-holes, are taken from each panel are placed under a conventional optical microscope of 50X magnification with a light source behind the samples.
• the quality of the copper deposits are determined by the amount of light visible under the microscope that is transmitted through the sample. Inside the plated through-holes, transmitted light is only visible in areas where there is incomplete electroless coverage. If no light is transmitted and the section appears completely black, it is rated a 5 on the backlight scale indicating complete copper coverage of the through-hole wall.

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